Hydrocarbon sweetening process



this corrosiveness.

nited States Patent 3,063,935 HYDROCARBON SWEETENING PROCESS Willem E.Nieuwenhuis, The Hague, Netherlands, as-

signor to Shell Oil, Company, a corporation of Delaware No Drawing.Filed Sept. 1, 1960, Ser. No. 53,372

Claims priority, application Netherlands Sept. 8, 1959 9 Claims. (Cl.203-204) This invention deals with the removal of mercaptans from liquidhydrocarbons, and more particularly relates to the preparation ofsubstantially non-corrosive, mercaptan-free, hydrocarbon oil.

It is known to free light hydrocarbon oils, such as gasoline andkerosene, from mercaptans by treating these oils with an aqueous alkalimetal hydroxide solution. In this treatment the mercaptans are extractedby the alkali.

metal hydroxide solution and converted into mercaptides.

If desired, this treatment may be carried out in the presence of oxygen,in which case the mercaptides are oxidized to disulfides. The latter areoil-soluble and pass from the aqueous alkali metal hydroxide solution tothe hydrocarbon oil.

In order to increase the extractive power of the'alkali metal hydroxidesolution, a solubility promoter, a solutizer, may be dissolved in thesolution. Examples of suitable solutizers are amino and hydroxyl alkylamines in which the alkyl groups contain 2 to 3 carbon atoms, glycols,amino glycols and diamino glycols having from 3 to 5 carbon atoms,diamino, dihydroxy or amino hydroxy dialkyl ethers or thioethers inwhich the alkyl groups contain 2 or 3 carbon atoms, alkali metal salts,in particular potassium salts, of fatty acids having from 3 to 5 carbonatoms, such as isobutyric acid, or hydroxy or amino fatty acids havingfrom 4 to 7 carbon atoms, or phenyl acetic acid, or hydroxy phenylacetic acid or amino phenyl acetic acid, alkyl phenolates, and mixturesof two or more of the above compounds.

If the mercaptan removal is carried out in the presence of oxygen, it isknown that aqueous alkali metal hydroxide solutions containing aphenolate as a solutizer may be employed, thereby increasing theextractive power of the solution for mercaptans. It may also beadvisable to 'add an auxiliary substance to the alkali metal hydroxidesolution in order to promote the solvent for oxygen. For examples,alkali metal hydroxide solutions containing solutizers are used whichcontain acetic acid and formic acid to increase the solvent power foroxygen.

The processes discussed above are generally not carried out to theextent where all mercaptans are removed from the hydrocarbon oil. Forpractical purposes it is suflicient to reduce the mercaptan content sothat the treated product is free from any offensive mercaptan odors, forexample, a mercaptan sulfur content of less than 20 ppm. would besatisfactory.

The processes set forth above, while quite effective in For example,when treated in accordance with the above method, a hydrocarbon oilwould be substantially mercaptan-free while having a marked corrosivetendency towards copper even where the parent product was noncorrosive.

It is a principal object of this invention to eliminate tion incorrosiveness is achieved by adding a quantity of mercaptan-containinghydrocarbon oil, which is non-copper-corrosive, to the mercaptan-freehydrocarbon oils A which have been treated in accordance with the abovprocesses.

The invention therefore relates to a process for the It has beendiscovered that a reducice preparation of a substantiallymercaptan-free, light hydrocarbon oil which is not corrosive to copper,by treating a light hydrocarbon oil containing mercaptans with anaqueous alkali metal hydroxide solution, which may contain one or moresolutizers to increase the extractive power for mercaptans to reduce themercaptan content to a small amount and adding a quantity of amercaptancontaining hydrocarbon oil which is non-copper-corrosive to thetreated light hydrocarbon oil to produce a blended product which isnon-corrosive to copper.

In the present specification the hydrocarbon oil is termed corrosive tocopper, viz., copper positive, when the corrosion test according toA.S.T.M. method D130, i.e., the copper strip corrosion test, isclassified as 2A or lower. The hydrocarbon oil is considerednon-coppercorr-osive, viz., copper negative, when the result of thecorrosion test is classified as 1B or higher.

It follows from two tests set forth below that compounds with oxidizingproperties are not responsible for the corrosiveness. The startingmaterial used in the first test was a catalytically' cracked gasolinepre-washed with a caustic alkali solution in order to remove hydrogensulfide and the like and with a mercaptan sulfur content of 74 ppm. Thisgasoline was successively subjected to 4 extractions with an aqueouscaustic alkali solution containing 650 g./l. of potassium hydroxide andg./l. of cresol (as cresolate). The copper strip corrosion test(A.S.T.M. method D) gave the following results:

Mercaptans, Copper Number of Extractions p.p.m. Strip 8 2B2C 4 2A 2 1BIt was found that the original gasoline which was noncopper-corrosive,viz., copper negative (1A) has become copper positive (2C) after thefirst extraction and'remained so after the second and third extraction,but after the fourth extraction the gasoline had'become copper negativelB) again. This test showed that the gasoline originally containedcorrosive compounds which apparently were inhibited by compoundssubsequently preferentially extracted by the caustic alkali solution.When the extraction was continued it was found that the corrosivecompounds were removed as well; the mercaptan content, however, is thenalso reduced to practially nil (2 p.p.m.).

This test, which was carried out in the absence of an oxidizing agent,shows that the corrosive properties which the hydrocarbon oil exhibitsafter an extractive mercaptan reduction are attributable to compoundswith oxidizing properties. in order to demonstrate'this a second testwas carried out with a copper-positive gasoline obtained by treating acopper-negative gasoline, in the presence of oxygen, with an aqueousalkali metal hydroxide solution containing a solutizer to increase theextractive power for mercaptans. When adding copper-negative gasolinecontaining mercaptans to the treated copperpositive gasoline acopper-negative mixture was obtained. The analytically determinedmercaptan content showed that in the mixture no mercaptans wereconverted, which would have been the case if compounds with oxidizingproperties had been present in the copper-positive portion.

The present invention is therefore based on the new and surprisinginsight that a copper-negative light hydrocarbon oil containingmercaptans may naturally contain copper-corrosive compounds which areinhibited by materials originally present in the hydrocarbon oil. Whenthe mercaptans are extracted by means of an aqueous alkali metalhydroxide solution these inhibiting compounds are found to bepreferentially extracted, thereby disturbing the ratio ofcopper-corrosive compounds to inhibiting compounds and causing thecopper-negative hydrocarbon oil to become copper-corrosive. Since thecopper-corrosive compounds are also extracted simultaneously, althoughto a lesser extent, it is possible to eliminate the copper corrosivenessof a hydrocarbon oil substantially free from mercaptans by adding arelatively small quantity of copper-negative hydrocarbon oil.

It should be noted that it is not known what compounds are responsiblefor the corrosive or the inhibiting properties, although it follows fromthe above that these compounds are very similar to the aliphaticmercaptans, as far as their extractive behavior with respect to anaqueous alkali metal hydroxide solution is concerned, the inhibitingcompounds being found to be more readily extractable than the corrosivecompounds.

The present copper-corrosiveness is not caused by free sulfur, as shownby the following test calried out with a copper-positive gasolineused'as a starting material in the second test described above. Thisgasoline contained 17 p.p.m. of'mercaptan sulfur and showed a copperstrip 23. After treatment with a sodium sulfide solution to remove anyfree sulfur present both the mercaptan sulfur content and the copperstrip were found to be unaltered.

disclosed by the first test described above, it is possible to prepare acopper-negative hydrocarbon oil by subjecting the starting hydrocarbonoil to a sufficiently drastic extraction treatment wherein the resultingmercaptan-sulfur content is practically nil (2 p.p.m.) Since all typesof mercaptans are not equally as readily extractable, with the tertiarymercaptans in particular being very diflicult to remove, it is neitherattractive nor practical to attempt such a treatment of the hydrocarbonoil in the refinery. This would necessitate a much larger installationand a considerably longer treatment. As regards the practicalrequirements with respect to the mercaptan-sulfur content of lighthydrocarbon oils, removal to a level of approximately -20 p.p.m. isgenerally suflicient. Such a partial removal of mercaptans can beefiected in a considerably simpler manner and according to the presentinvention, this removal need only be carried out to such an extent thatthe final mercaptansulfur content of the copper-negative mixture,obtained by adding a quantity of non-corrosive mercaptan-containinghydrocarbon oil to a hydrocarbon oil partly freed from mercaptans, doesnot exceed the above-mentioned limit of approximately 5-20 p.p.m. and isthus free of an offensive mercaptan odor.

The non-copper-corrosive starting hydrocarbon oil will generally be usedas inhibiting agent for the coppercorrosive hydrocarbon oil which ispartly free from mercaptans, although other coppernegative hydrocarbonoils may be used. Particularly suitable mercaptan-containing hydrocarbonoils are those obtained by straight-run distillation. The use of an oilother than the starting hydrocarbon .oil may lead to technical andeconomic advan- V tages, for instance when a quantity of acopper-negative,

mercaptan-containing butane and/ or butylene fraction (socalled Cfraction) and/or pentane and/ or pentane-conraining fraction (so-calledC fraction) is added to a copper-positive gasoline. The addition of suchfractions is often necessary in the refinery to obtain a sufficientlyvolatile motor gasoline; in this case the mercaptans are previouslycompletely or partly removed from these fractions. The addition of a Cand/or C fraction containing mercaptans as inhibiting agent maytherefore make it unnecessary to use a separate installation for theremoval of the mercaptans from these fractions.

In treating a copper-negative hydrocarbon oil with an aqueous alkalimetal hydroxide solution the inhibiting components are preferentiallyextracted from the hydrocarbon oil and the extract phase will contain arelatively high concentration of inhibiting components. It may thereforebe advantageous to introduce a portion of the extract as inhibitor inplace of the starting hydrocarbon oil. A mixture of anon-copper-corrosive hydrocarbon oil and an extract may also be used asthe inhibiting agent.

The phenomenon of copper-corrosiveness of a light hydrocarbon oil aftera treatment with an aqueous alkali metal hydroxide solution is morepronounced in hydro carbon oils obtained by cracking. It occasionallyoccurs that the light hydrocarbon oil is copper-corrosive even beforethe extractive treatment for the removal of mercaptans. A startingproduct of this nature cannot be used to eliminate thecopper-corrosiveness of the oil treated with an aqueous alkali metalhydroxide solution. In this case it will be necessary to use a differentlight hydrocarbon oil containing mercaptans, which is actuallycopper-negative, or an extract therefrom. The occurrence ofcopper-corrosive hydrocarbon oils prior to mercaptan extractionindicates that differences may also be expected in the copper-negativestarting oils with respect to the content of inhibiting components,viz., the content of corrosive components. It therefore follows that itwill be necessary to determine experimentally in each particular casethe quantity of untreated hydrocarbon oil, or of inhibiting extractrespectively, necessary to modify the copper-positive product into acopper-negative oil.

It has been found that in most cases a copper-negative final product maybe obtained by mixing the product which is partly freed from mercaptanswith less than 30% by volume of a non-copper-corrosive hydrocarbon oilcontaining mercaptans. This determines the extent of mercaptanremovalnecessary to give a fiinal product which has the desired mercaptancontent after addition of less than 30% by volume of thenon-copper-corrosive hydrocarbon oil. If, for instance, parts by volumeof alight hydrocarbon oil containing 50 p.p.m. of mercaptan sulfur isused as starting material, it will be necessary to desulfurize this oilto 10 p.p.m. in order to obtain a final product with a content of 15p.p.m. of mercaptan sulfur after addition of 10 parts by volume of thestarting hydrocarbon oil. In many cases a copper-negative final productmay be obtained by adding 1-20% by volume of a non-copper-corrosivehydrocarbon oil containing mercaptans and as a rule the quantity to beadded will vary from 6 to 12% by volume. Instead of non-copperco'rrosivehydrocarbon oil, a corresponding quantity of extract from anon-copper-corrosive hydrocarbon oil may be added; will be appreciatedthat a mixture of the noncopper-corrosive hydrocarbon oil and an extractmay also be employed.

The process may be applied to light hydrocarbon ds (viz., hydrocarbonoils with a boiling range of 40-350 in particular mercaptan-containinggasolines and kerosenes of different origin. For example, gasoline andkerosene obtained by straight-run distillation of crude oil and gasolineand kerosene produced by thermal or catalytic cracking of heavierfeedstocks.

It is a preferred embodiment of this invention to remove first any acidspresent in the hydrocarbon oils by means of a dilute aqueous alkalimetal hydroxide solution. These acids are stronger than the mercaptansand are removed before the mercaptans according to the process of thepresent invention. A pretreatment with dilute caustic alkali solutionhas an additional advantage in that any thiophenols which may be presentand possess a considerably stronger acidic character than aliphaticmercaptans, are removed, at least in a considerable quantity, from thehydrocarbon oil prior to treatment. Since thiophenols occur especiallyin light hydrocarbon oils obtalned by orackingheavier hydrocarbons, andparticularly in products obtained by catalytic cracking, a pretreatmentwith dilutecaustic alkali solution is especially suitable for suchproducts. This pretreatment is preferably carried out before the crackedproducts come into contact with oxygen or an oxygen-containing gas toprevent possible gum formation.

The removal of mercaptans from hydrocarbon oils by means of an equeousalkali metal hydroxide solution in the presence of oxygen results in theformation of disulfides which pass into the hydrocarbon oil. Thereforethis process is primarily suitable for treating hydrocarbon oils with alow mercaptan content, i.e., lower than 500 p.p.m. and preferably lowerthan 200 p.p.m., calculated as mercaptan sulfur. In this instance thequantity of disulfides taken up in the hydrocarbon oil would berelatively low.

When a hydrocarbon oil with a considerable mercaptansulfur content, forinstance 500 p.p.m. or more, is to be freed from mercaptans, it ispossible first to remove the greater portion of the mercaptans, togetherwith other sulfur compounds, by means of an aqueous alkali metalhydroxide solution, which may or may not contain one or more solutizersto increase the extractive power for mercaptans, and then to reduce themercaptan content by converting them, in the presence of oxygen, intodisulfides by means of an alkali metal hydroxide solution which maycontain one or more auxiliary substances and solutizers.

When the process carried out in the presence of oxygen is applied tocatalytically cracked hydrocarbon oils containing unsaturated compounds,an anti-oxidant is preferably added to the oil to prevent gum formationby the unsaturated components of the oil. In general a quantity of 1200p.p.m. of such an anti-oxidant is sufficient.

Example I The starting material was a catalytically cracked gasolinewith a boiling range of 40-165 C. (A.S.T.M.) and containing 100 p.p.m.of thiophenol sulfur, 50 p.p.m. of alkyl phenols and 90 p.p.m. of alkylmercaptan sulfur. This gasoline was treated with 1% by volume of a 20%aqueous sodium hydroxide solution at a temperature of 30 C. to removethe thiophenols and a portion of the alkyl phenols. After this treatmentthe thiophenol sulfur content was nil, the alkyl phenol content 35p.p.m. and the alkyl mercaptan sulfur content 70 p.p.m. The gasoline,which was copper-negative (copper strip corrosion test 1A), was thenpassed into a propeller mixer at a temperature of 30 C. in a quantity of1600 tons/day, the impeller speed being 400 rpm, 32 0 tons/day oftreating liquid consisting of 35% by weight of technical cresol, 33% byweight of potassium hydroxide and 34% by weight of water were alsocontinuously supplied to this propeller mixer. In addition, air wasblown into the gasoline supply line in a quantity corresponding to 200%of the quantity of oxygen theoretically required for the oxidation ofthe mercaptans present.

The mixture of gasoline and aqueous solution discharged from the mixerwas passed into a settling space in which the two phases separated. Theaqueous solution was continuously recycled to the mixer. The separatedgasoline, which was copper-positive (copper strip corrosion test 2C) andcontained 11 p.p.m. of mercaptan sulfur, was continuously dischargedfrom the settling space and mixed with 1 60 tons/day of the startinggasoline from which the thiophenols had been removed 'by a pretreatmentwith aqueous sodium hydroxide solution (as above). The resultantgasoline mixture was copper-negative (copper strip corrosion test 1A)and contained 16 p.p.m. of mercaptan sulfur.

Example 11 A catalytically cracked gasoline was treated in the samemanner as described in Example I and 'had a copper strip test value of1A after washing with a 20% aqueous sodium hydroxide solution and amercaptain sulfur content of 61 p.p.m. The gasoline discharged from thesettling space had a copper strip 2B and a mercaptan sulfur content of17 p.p.m.

After addition of 5% by volume of the starting product washed withsodium hydroxide solution, the mixture had a copper strip lA-lB and amercaptan sulfur content of 10 p.p.m.

Example III 1% by volume of a gasoline obtained by thermal cracking wasadded to the same gasoline as in Example II which, after the treatmentfor removing mercaptans,

showed a copperstrip 2B and had a mercaptan sulfur content of 17 p.p.m.After washing with 20% sodium hydroxide solution this gasoline had acopper strip 1A and a mercaptan sulfur content of 3 p.p.m.

After addition of this gasoline the mixture had a copper strip 1A and amercaptan sulfur content of 20 p.p.m.

I claim as my invention:

1. A process for preparing a substantially mercaptanfree,non-copper-corrosive light hydrocarbon oil, comprising treating a lighthydrocarbon oil, containing mercaptans, with an aqueous alkali metalhydroxide solution containing a solutizer for mercaptans andsubsequently separating the treated light hydrocarbon oil, substantiallyfree of mercaptans and displaying copper corrosiveness, from the alkalisolution andadding a suflicient amount of a non-copper-corrosive, lighthydrocarbon oil containing mercaptans to the treated hydrocarbon oil toproduce a substantially mercaptan-free light hydrocarbon oil showing nocorrosiveness to copper.

2. The process of claim 1 wherein the treatment with the aqueous alkalimetal hydroxide solution is carried out in the presence of oxygen andwherein the hydroxide solution contains an additional substance topromote the solvent power for oxygen.

3. The process of claim 1 wherein the starting material is used as thenon-copper-corrosive hydrocarbon oil containing mercaptans which areadded to the treated hydrocarbon oil.

4. The process of claim 1 wherein an extract from a non-copper-corrosivestraight-run hydrocarbon oil containing mercaptan is the material addedto the treated hydrocarbon oil.

5. The process of claim 1 wherein a non-copper-corrosive, hydrocarbonoil containing mercaptans which has been treated with a dilute aqueousalkali metal hydroxide solution to remove hydrogen sulfide andthiophenols, is the material added to the treated hydrocarbon oil.

6. The process of claim 1 wherein 1 to 20% by volume of anon-copper-corrosive, hydrocarbon oil containing mercaptans is thequantity of material added to the treated hydrocarbon oil.

7. The process of claim 1 wherein 1 to 20% by volume of an extract of anon-copper-corrosive, hydrocarbon oil containing mercaptans is thequantity of material added to the treated hydrocarbon oil.

8. The process of claim 1 wherein 6 to 12% by volume of anon-copper-corrosive hydrocarbon oil containing mercaptans is thequantity of material added to the treated hydrocarbon oil.

9. The process of claim 1 wherein the light hydrocarbon oil containingmercaptan used as a starting material is obtained by catalytic cracking.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR PREPARING A SUBSTANTIALLY MERCAPTANFREE,NON-COPPER-CORROSIVE LIGHT HYDROCARBON OIL, COMPRISING TREATING A LIGHTHYDROCARBON OIL, CONTAINING MERCAPTANS, WITH AN AQUEOUS ALKALI METALHYDROXIDE SOLUTION CONTAINING A SOLUTIZER FOR MERCAPTANS ANDSUBSEQUENTLY SEPARATING THE TREATED LIGHT HYDROCARBON OIL, SUBSTANTIALLYFREE OF MERCAPTANS AND DISPLAYING COPPER CORROSIVENESS, FROM THE ALKALISOLUTION AND ADDING A SUFFICIENT AMOUNT OF A NON-COPPER-CORROSIVE, LIGHTHYDROCARBON OIL TO PRODUCE ING MERCAPTANS TO THE TREATED HYDROCARBON OILTO PRODUCE A SUBSTANTIALLY MERCAPTAN-FREE LIGHT HYDROCARBON OIL SHOWINGNO CORROSIVENESS TO COPPER.